Prior art methods of coating articles with polymers include the process of vapor deposition. Parylene is an excellent polymer for coating articles due to its ability to form thin surface films and to conform to articles of various shapes and surface configurations. Parylene is particularly suited for coating wires and wire-type parts of various lengths and diameters due to such coating properties. Parylene is typically applied to the surfaces of articles by the process of vapor deposition conducted under vacuum conditions in a coating apparatus. The parylene dimer is first vaporized to a gaseous state and then pyrolitically cleaved to form reactive monomer parylene vapors. The monomer parylene vapors are transferred to and circulate within a coating chamber of the coating apparatus in which articles to be coated are contained. As the monomer vapors contact the surfaces of the articles, the vapors condense on the surfaces and polymerize to form a surface film or coating of parylene on the articles. Such a deposition coating process is an excellent method of coating wire-type articles and wire parts on which even surface films or coatings are difficult to achieve. This is particularly the case when coating when coating large quantities or bulk loads of wire-type articles and wire parts by a vapor deposition process.
Prior art devices for coating articles by vapor deposition include a drum-type apparatus, as disclosed in U.S. Pat. No. 4,758,288, wherein articles are placed in a coating drum which rotates and tumbles articles during the coating process. A disadvantage of this coating apparatus is that parylene vapors must be introduced into the drum by means of a feed tube. As the vapor deposition coating process is conducted under vacuum conditions, pressure gradients may be created within the drum and also between the drum and the external atmosphere in which parylene vapors circulate. Pressure gradients cause an uneven circulation of parylene vapors which results in uneven depositing of parylene vapors on the surfaces of articles and uneven and inconsistent surface films. In addition, the coating apparatus is not conducive to coating large quantities or bulk loads of articles due to mechanical damage to surface films cause by the weight of large quantities or bulk loads.
The basket-type cellular apparatus disclosed in U.S. Pat. No. 5,201,956, assigned to the assignee of the present application, is an improvement upon the drum-type apparatus, wherein a plurality of basket-type cells with multiple side wall throughholes are configured about a common axis of rotation. The side wall throughholes put articles contained therein in close communication with circulating parylene vapors as the basket-type cells are rotated during the coating process. Although an improvement over prior art devices, the basket-type cellular apparatus is not by itself always a suitable means for coating large quantities or bulk loads of articles, particularly large or bulk loads of wire-type articles and wire parts.
Other prior art devices for coating wire-type articles and wire parts by parylene vapor deposition include manually mounting individual articles in a static position to a fixture plate contained within a coating chamber of a coating apparatus. For example, mounting wire parts to the fixture plate enables individual wire parts to hang freely, exposing the surfaces of the wire parts to parylene vapors which circulate in the atmosphere within the coating chamber. However, the wire parts must be sufficiently spaced apart to prevent adjacent wire parts from touching or adhering together. Insufficient space between individual wire parts can cause an uneven deposition of parylene which forms inconsistent surface films on the wire parts or results in portions of the surfaces of the wire parts to remain uncoated. The spatial arrangement required insure thorough and even parylene deposition and ultimately even and consistent surface films or coatings involves significant manual handling and fixturing to appropriately space and mount individual wire parts to the fixture plate. Manually mounting and removing individual wire parts in this manner is a labor intensive practice which reduces the efficiency of this coating process.
As a result, the use of a device such as the fixture plate to properly arrange wire parts for deposition coating results in a low parts per load ratio. This coating process is also a static method of coating, wherein the wire parts remain stationary during the coating process. Such a static process, therefore, is highly dependent upon achieving an adequate circulation of parylene vapors and susceptible to pressure gradients which may occur in the atmosphere of the coating apparatus.
Therefore, it is desirable to have a vapor deposition coating apparatus and method which reduces or eliminates the need for manual handling and fixturing of articles, and which increases the parts per load ratio of prior art devices, particularly with respect to coating wire-type articles and wire parts. In addition, it is also desirable to reduce the susceptibility of the coating apparatus and method to pressure gradients during the coating process by adequately exposing the surfaces of the articles to be coated, while preventing the articles from sticking or becoming coated together. In addition, it is desirable to provide a vapor deposition coating apparatus and method for surface coating large quantities or bulk loads of articles, and particularly large quantities or bulk loads of wire-type articles and wire parts, which produces even and consistent surface films.